While highly active anti-retroviral therapy (HAART) can suppress HIV-1 replication, treatment currently does not eradicate infection or prevent a low level of continued replication. The major objective of this project is directed to defining the anatomic and cellular compartments in which HIV-1 is produced and persists before and during HAART, and from which infection re-emerges on discontinuation of HAART. The Specific Aim of the project is to identify, characterize and quantify cellular sources of virus production and persistence in gutassociated lymphatic tissues (GALT) and peripheral lymphatic tissues (LTs), using state-of-the-art in situ Technologies of in situ hybridization, in situ PCR, immunohistochemistry and quantitative image analysis, with the long-term goal of capitalizing on the new insights into HIV-1 reservoirs generated by this analysis to design even more effective treatments.